1. Field of the Invention
The present invention relates to proton exchange membrane fuel cells, and particularly to a fuel cell membrane for proton exchange membrane fuel cells formed from a blend of sulfonated poly(ether ether ketone) (SPEEK) and phosphonated polysulfone in the ester form (PPSU-E).
2. Description of the Related Art
Proton exchange membrane fuel cells, also known as polymer electrolyte membrane (PEM) (or polyelectrolyte membrane) fuel cells (PEMFCs), are a type of fuel cell presently being developed for transportation applications, as well as for stationary fuel cell applications and portable fuel cell applications. Their distinguishing features include lower temperature/pressure ranges (50° C. to 100° C.) and a special polymer electrolyte membrane. PEMFCs operate on a similar principle to polymer electrolyte membrane electrolysis. FIG. 2 illustrates a typical proton exchange membrane fuel cell 10. Gaseous hydrogen fuel is channeled through outer field flow plates 12 to the anode 14 (on one side of the fuel cell 10) and to the cathode 16 (on the other side of fuel cell 10). At the same time, an oxidant, such as oxygen gas or air, is channeled to the cathode 16. At anode 14, a platinum catalyst causes the hydrogen to split into positive hydrogen ions (i.e., protons) and negatively charged electrons.
The polymer electrolyte membrane (PEM) 18 allows only the positively charged ions to pass through it to the cathode 16. The negatively charged electrons must travel along an external circuit to the cathode 16 (illustrated in FIG. 2 with an exemplary simple light bulb L connected across the hydrogen flow fields 12), creating an electrical current. At the cathode 16, the electrons and positively charged hydrogen ions combine with oxygen to form water, which flows out of the cell.
Nafion®, manufactured by EL DuPont De Nemours and Company of Wilmington, Del., is a common ionomer used in proton exchange membrane fuel cells. Nafion® is a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer, with its ionic properties being the result of incorporating perfluorovinyl ether groups terminated with sulfonate groups onto a tetrafluoroethylene backbone. Nafion® was found effective as a membrane for proton exchange membrane fuel cells by permitting hydrogen ion transport while preventing electron conduction. However, Nafion® dehydrates (thus losing proton conductivity) when temperatures are above ˜80° C. This limitation causes problems in the design of fuel cells, because higher temperatures are desirable for a better efficiency and CO tolerance of the platinum catalyst.
Thus, a fuel cell membrane solving the aforementioned problems is desired.